In recent years, an idle reduction coasting technology is required in order to improve a fuel economy, in which an internal combustion engine (referred to as an engine) is stopped and a coasting is performed.
In Patent Literature 1, when a restart requirement for an engine is generated while a vehicle is coasting, and a rotational variation of an output shaft connected to a driving wheel is higher than a set value, a clutch is connected to an output shaft of the engine so that an rotation speed of the engine is increased by a driving force which a running vehicle has, whereby the engine is restarted (referred to as a push-start). Moreover, when the rotational variation of the output shaft is lower than the set value, the engine is started by a starter motor.
In a vehicle provided with such an idle reduction coasting technology, since the engine may be stopped while a vehicle is running at high speed, it is required to surely perform a restart of the engine. However, the restart of the engine by the push-start described in Patent Literature 1 is not always ensured. Similarly, the restart of the engine by the starter motor is not always ensured.